Nitride-based films are widely used in semiconductor devices and ultra-large-scale integrated (ULSI) circuits. For example, nitride films have been widely used in semiconductor devices as diffusion barriers for dopants and metals, as an etch-stop film during etching of fine features, as a final passivation film for encapsulation of fabricated devices, and as electrodes in capacitor and metal-oxide semiconductor field-effect transistor (MOSFET) structures, among many other uses. Nitride films can be deposited at low pressure or at atmospheric pressure using a variety of processing systems and process gases.
Recent innovations to improve complementary metal oxide semiconductor (CMOS) transistor performance have created an industry need for strained films that are compatible with current ULSI integration techniques. In particular, channel carrier mobility for negative metal oxide semiconductor (NMOS) transistors can be increased through introduction of tensile uniaxial or biaxial strain on a channel region of a MOS transistor. Typically, this has been accomplished by deposition of highly tensile strained silicon nitride films that are compatible with existing fabrication processes. With the advent of metal gate stacks, the strain imparted in the channel using stressed silicon nitride liner films over the MOSFET will be decreased due to the higher modulus of the metallic films. One proposed solution to this problem is to use stressed films within the gate stack, so that the stressed film is more proximate to the channel, thus increasing the imparted strain.